Ruth Davidson is facing renewed pressure to stand down as an MSP over her decision to accept a £50,000 a year "second job" with a PR firm after her position was branded "untenable".
The ex-Tory leader has come under fire over the decision to take on the job with Tulchan Communications for 24 days work a year.
Read more: Euan McColm: Every day Ruth Davidson remains an MSP will only increase damage to her party
George McGregor, co-chair of the UK Public Affairs Board at the Public Relations and Communications Association (PRCA), has become the latest industry leader to voice his criticism over the move and urged Ms Davidson to stand down as an MSP.
"Ruth Davidson should stand down as an MSP if she wants to join the ranks of the public affairs industry," Mr McGregor said on Twitter.
He added: “The rules are there for a reason: to avoid any conflicts of interest both in perception and reality.”
Read more: Ruth Davidson faces pressure to quit as MSP after setting up her own PR firm
Ms Davidson's decision has provoked widespread controversy, but has sought to defend her position.
A Scottish Conservative spokesman said: "Ruth sat down with Scottish Parliamentary officials before considering this position and went through the code of conduct in detail.
“The role in question involves no lobbying and falls well within the rules.
“She encourages anyone who believes a breach may have taken place to refer her to the standards commissioner for a ruling and has restated her commitment to serving out her term as the MSP for Edinburgh Central."
But SNP MSP Gordon MacDonald there is now "immense pressure" on Ms Davidson to resign as an MSP.
"Questions over her new £50k-a-year-role with a lobbying firm will continue to grow until she does the right thing and quits Holyrood," he said.
“These latest comments, coming from the chair of an industry body, are an utterly damning indictment of her position, which is now completely untenable."
Ms Davidson stood as Scottish Tory leader in August as she admitted being "hopelessly conflicted" over Brexit and is not expected to stand again at the next Holyrood election in 2021.